my guess will be filters smaller than 77mmmaybe 67mm? all plastic construction

I doubt it'll be an all plastic construction simply because of its L designation.

From Wikipedia:Most L series lenses share a number of common characteristics:- Tough build, made to withstand trials in the field (some incorporating dust and moisture resistant rubber seals).- At least one fluorite or ultra-low dispersion glass element, combined with super-low dispersion glass and ground aspherical elements.- Non-rotating front elements, which are optimal for some filters (e.g. circular polarizers).- Relatively large apertures compared to other Canon lenses in the same focal lengths.- Ring-type USM (ultrasonic motor) and full-time manual focusing.

You must have missed the 100 f2.8L IS Macro and 24-70 f2.8L II both are engineering plastics....

6) This new lens will replace the 24-105, eliminating the 70-105 overlap that current lens has. This is a deliberate move by Canon to sell more 70-200 glass. (I have poked a few holes in this theory, but it's as plausible as anything else on this list).

Eliminating the 24-105 would certainly be a consumer hostile move. The focal length overlap certainly did not stop me from getting a 70-200. The overlap is extremely useful in my work. There are some jobs I do pretty much entirely with the 24-105, whereas if I had the 24-70 (one of the least interesting focal ranges I can imagine - my opinion only), I'd do a lot of switching between the two lenses.

Someone earlier called the 24-105 "slow." Could not disagree more. I use it all the time for basketball in gyms with permanently mounted studio flashes or with my own flashes temporarily mounted. On the 7D, I have ideal reach all the way from right under the goal to three-point land. The f/4.0 max aperture does make manual focus difficult or near impossible, but fortunately, I get a near 100% AF hit rate.

I'd look at this rumored 24-70 as a secondary lens, possibly for remote mounted use or when more compactness is desired, such as for recreational shooting, especially if it addresses the 24-105's minor optical shortcomings (distortion/curvature at edges).

I admit I am getting confused here. I planned on selling my 24-105 to a friend to get a new 24-70 Mark II, but now I am caught in between waiting for a possible 24-70 f2.8 IS and not wanting to replace my 24-105 with a 24-70 f4 IS and maybe, just maybe, purchasing a second 24-105 just in case it gets eliminated from the lineup. This is annoying. The only thing for sure is that this 24-70 f4L IS is not for me.

I admit I am getting confused here. I planned on selling my 24-105 to a friend to get a new 24-70 Mark II, but now I am caught in between waiting for a possible 24-70 f2.8 IS and not wanting to replace my 24-105 with a 24-70 f4 IS and maybe, just maybe, purchasing a second 24-105 just in case it gets eliminated from the lineup. This is annoying. The only thing for sure is that this 24-70 f4L IS is not for me.

If it makes it any easier for you... I got a 24-70 f2.8 mk.ii and was not blown away by the IQ (compared to the mighty 70-200 mk.ii). It was nice and F2.8... and AF was fast... but I Paid more for it than the tele, it has no IS, the lens elements were not 100% aligned (asymmetric vignetting)... so unless they sold it for $1500-1700, I wont miss it much. I have a 17-40 and a 70-200, there is not a whol lot between 40mm and 70 than a nice 50mm prime could not cover...

I don't get it. What would I do with such a lens? I see some value in the 24-105 due to the flexible focal length. For that I'm willing to put up with f/4 and IS under certain circumstances. Yes, IS to me is a negative not a plus. Same for 24-70? No way. Nothing gained there.

my guess will be filters smaller than 77mmmaybe 67mm? all plastic construction

I doubt it'll be an all plastic construction simply because of its L designation.

From Wikipedia:Most L series lenses share a number of common characteristics:- Tough build, made to withstand trials in the field (some incorporating dust and moisture resistant rubber seals).- At least one fluorite or ultra-low dispersion glass element, combined with super-low dispersion glass and ground aspherical elements.- Non-rotating front elements, which are optimal for some filters (e.g. circular polarizers).- Relatively large apertures compared to other Canon lenses in the same focal lengths.- Ring-type USM (ultrasonic motor) and full-time manual focusing.

You must have missed the 100 f2.8L IS Macro and 24-70 f2.8L II both are engineering plastics....

Yep. Wikipedia is wrong about this. Most L lenses in fact are plastic. I may be wrong but of the more recent lenses I think only the original 24-70 had a metal barrel (and then some plastic parts in key areas anyway) - and probably some of the big white tele lenses and zooms I'd think.But as much as I like my 50L and 135L: plastic and I treat them like raw eggs. Even the filter threads are plastic on all lenses these days. Those feel and handle better than my rather flimsy 24-105, but still. Non of this compares to the feel and sturdiness of my old FD lenses.

I found the LensRentals review of the 24-70ii most interesting concerning the "sturdiness" because Roger pointed out that the mk1 might be metal, but at the same time it's more fragile than the mk2 because the older lens is much more prone to decentering when taking a hit.

So when not always thinking of the worst-case scenario (lens or body falls from a skyscraper and is overrun by a truck) a newer plastic construction might outmatch an older/cheaper metal one in real world usage. But I'd still like my 100L to be metal :-p

I somewhat doubt Canon will kill the 24-105 completely. Maybe they'll replace it with a 24-120 or something, while the 24-70 becomes the lens for more size- and weight-conscious shooters. When I travel, I take my 70-300L with me to capture wildlife photos, as well as a 15-85mm walk-around lens. If I had a full frame camera, I would gladly trade a 70-105mm overlap for lighter weight and smaller size to reduce the overall bulk of my backpack.

This means...-a new f4 wide angle-maybe a new 70-200 f4 is ii-maybe a 70-200 2.8 is iii

Maybe canon is using special glass, for the 24-105, they had to compromise on glass quality, I think since everyone wants a 24-70, they'll give a budget one, with good glass.

This could be a competitor for the tamron 24-70 vc, so people have to decide, tamron 2.8, or canon sharpness and build quality. With the Iso capabilities of canon dslrs, f4 won't be an issue, this is probably going to be launched with the 6d.

I think the f/2.8 wide angle will be 14-24mm, but I think the f/4 will be 16-35 IS to directly compete in all aspects with the Nikon lens. That will make it wider than the current f/4, sharper (as pretty much all lenses have been over their predecessors) and likely more expensive. Hopefully, Canon will come out with cheaper variable aperture [or non-IS] UWA to replace the long-extinct 20-35mm f/3.5-4.5 USM for the lower end of the budget (~$500), as well. Think about this (as a beginner):